In recent years, hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and electric vehicles (EV) are being spread. In the vehicle, the power supply system is installed, which includes a plurality of power storage modules connected in series for supplying a drive power to a running motor. When the running motor requires high voltage, the increase of the voltage of the power supply system is carried out by increasing the number of series-connected power storage modules.
In the power supply system installed in the vehicle, when the vehicle is submerged or immersed in water or the leakage of a liquid coolant for cooling happens, there is a possibility, that adjacent storage batteries are directly short-circuited to each other, or the storage batteries are short-circuited through a metal box. When the arc discharge happens in the high electric potential difference, there is a possibility that a hole is opened in the battery can due to the arc discharge, and there is a risk that the electrolyte or the like leaks, resulting in ignition.